curtis



April 12,1927.

1,624,396 A. M. CURTIS SUBMARINB SIGNALING SYSTEM Filed Sepi. 17, 1925 s Sheets-Sheet 1 W by 1 4/7? 19 April 27 A. M. CURTIS SUBMARINE SIGNALING SYSTEM Filed Sept; 17, 1925 5 Sheets-Sheet 2 3 Sheets-Sheet 5 A. M. cuR'ns SUBMARINE SIGNALING SYSTEM Filed Sept. 1?. 1925 Frequency v53 =0 nnis April 12 1927.

Ti me Patented Apr. 12, 1927.

AUSIEN M. CURTIS, OF EAST ORANGE, IiTEW' JERSEY, ASSIGNOR TO WESTERN ELEC- TRIC CQMIPANY, INCOB-POBLMLED, OF NEW YORK, N. 1 A CORPORATION OF NEW YORK.

SUBMARINE SIGNALING SYSTEM.

Application filed September 1'7, 1925. Serial No. 56,855

This invention relates to submarine signaling; systems and more particularly to submarine signaling systems in which the terminal. equipment is arranged and designed to operate to permit the transmission oi signals over speeds.

It is an object of the invention to provide terminal equipment which improves the legibility oi the signals transmitted at high. signaling speeds.

It has heretofore been proposed to use auxiliary apparatus at the terminal of u submarine cable designed to operate upon the wave form of the signals and to so shape these wave forms as to increase the legibility oi. the signals as recorded at the terminal. Devices of this sort are generally referred to as shaping networks or shaping elements. Combinations of: apparatus tor this perticulur purpose in connection with submarine cables are disclosed in epplicents Patents 1.586370 and 1,586,972, both issued June 1, 1926.

The present invention is in the nature of an improvement on these shaping networlzs or elements and is particularly useful in handling code signals from to 60 cycles per second or higher.

in accordance with this feature the special slurp j element which cooperates with the sen g ap iiurutus takes the form of an impedance which has a. low value as mmpured with the characteristicimpedance ot' thecu'ble and which is in. effect, shunt )fitll to eurtln on both the cable and its :msot'isted trm'ismitter and shunted sending crmdenscr. At the receiving end of the cable the novel shaping clement takes the form of e highly dumped anti-resonant C11- cuit which is connected in series wlth. the

a submarine cable at high In accordance with a. feature of the invensignaling current path and tuned to :1 trequency somewhat below the signaling frequency.

In accordance with another feature of the invention and cooperating with. the shaping); element reiterred to as at the receiving end ot' the systen'i, there is provided input-o transformer which is associated with the receiving circuit through a combination of resistances which also performs a. shapine' function for currents of a somewhat dirferent range of "frequencies than those tor which the anti-resonant tuned circuit is effective.

These and other features oi the invention will more clearly appear from the following description and the accompanying drawings in which- F 1 and 2 when placed side by side show diagrammatically a complete sending and transmitting equipment in accordance with the invention, such as is located at one terminal oi. the cable;

Fig. 3 shows a section of loaded conductor;

Figs. 4, 5 and 6 are diagrammatic representations of various electrical conditions which occur in the system and will be used in explanation thereof;

F 7, 8 end 9 show modified forms of the receiving equipment, and

Fi l0 and 11 show modified transmitting arinngements.

. Due to the invention of an improved form of submarine cable and particularly to an improved loading material and methods of applying it to a cable it has become possible to operate at much higier signaling speeds than heretofore. This has necessitated the design and invcnlion of new receiving and sending equipment, us well as the new sheping net-works illustrated end claimed in the applications previously referred to.

As will more clearly appear from. the fol. lowing descriptioin the present invention. is concerned with the further improvement in shapingnetworks and shaping elements as app ied to this recently invented. equipment. The new result obtained by virtue of the present invention is, as above pointed out, the more complete and accurate shaping of the signals to permit the satisfactory transmission of code signals up to cycles or higher.

In the operation oi submarine telegraph cables, the signal is formed by impressing positive and negative impulses upon the cable in various combinations and, as a result, there is always some limiting frequency of transmitted impulses above which the received signals Will be unintelligible. This limiting frequency may be called the limiting signaling frequency and is expressed in cycles per second. By signaling frequency is meant the number of dot impulses trans mitted per second when a succession of alternate dot and dash impulses is sent at the designated frequency of operation.

These var ous combinations of positive and negative impulses with periods of zero current may have frequency components anywhere Within the range of from zero to in- However, in order to obtain sulficiently well formed signals at the receiver, such a wide range of frequencies is not actually required- Satisfactory results may be obtained provided all of the component frequencies up to about one and one-half times the signaling frequency are properly transmitted. Thus, for signaling frequencies of 60- ,to cycles, it is important to transmit "frequency components up to about 100 cycles and, it is particularly desirable to provide adequate shaping for these higher frequencies. especially when it is desired to transmit code messages where accuracy is essential.

Referring now to the drawings, it will be noted that the sending and receiving equipment at one terminal of the cable is, in general, similar to that disclosed in the applications herei-nbetore referred to in that it consists of the usual sending equipment in volving, in. addition to an instrumentality torplacing impulses on the cable, a sending condenser 19 with the usual shunt resistance 20, and the receiving equipment, in addition .to the shaping elements, includes a fourstage amplifier oi the vacuum tube type working into a recording device which may be a. specially designed high speed siphon recorder.

In order .to point out the construction and cooperation of the novel shapingelements ot'v the present invention with the usual transmitting and receiving equipment, the terminal apparatus will now he described in detail and the relation of the novel elements thereto will bepointed out as the description messes other end to a switch 8 by means of which it can be conncrted in its upper position to terminal 3 oi the signal receiving apparatus it extending to the right of line X-X and in its lower position to the transmitting apparatus T. The other core 9 of the twin core section 6 is connected at the sea end through a resistance 10 to a conductor in contact with the sea water. In the particular arrangement shown, the resistance is connected to the cable armor wires at point 11 and a conventional ground connection, shown by dotted lines, is used to indicate that the armor wires are grounded. The core 9. together with the network 10 grounded at the point 11. constitutes a cable balancing return circuit. The shore end oi core 9 is connected to terminal. -l of the receiving: apparatus R.

'Atype of core suitable for both the single core cable 5 and the twin core section 6 is illustrated in Fig. 3. The core comprises a copper conductor 14 provided with a wrapping 15 of a nickel-iron alloy, as described and claimed in patent to G. W. Elmcn 1,586,887, issued June 1, 1926. The advantage of using this loading material is that its permeability at small inzmmztiZing forces ot the order of 0.01 to 0.10 gauss is from 10 to 20 times that of iron, that is, from 2000 to 4000. Over the wrapping of nickel-iron. alloy, an insulating layer 10 of gutta percha or similar material is applied. The cable, with which the terminal :upparatus, herein described, is intended to operate, when protected by armor wires in accordance with standard submarine cable practice. has a characteristic impedance for the higher frequencies involved in signaling of approximately 400 ohms, and this impedance is substantially a pure resistance.

The transmitting equipment T coinprises a positive and negative impulse transmitter 17. series resistance 18 of .10 to 50 ohms, and condenser 19 of 20 to 7? microfarads with shunting resistance 520 of 5,000 to 100,000 ohms. Ashereiubetore explained. the transmitting equipn'lent T may be connected to the core 7 of the twin core section 6 by means of switch 8 in its lower position. One terminal of the trausmitthuy equipment is thus connected to the core 7. while the other terminal is grounded at a beach earth 2 or through a short length of low resistance conductor at an extra earth at sea. According; to one Feature oi this invention a comparatirel low resistance J1 oi 50 to 200 ohms is connecieiil between the loo it is evident that for the voltages of very low frequencies this can not be the case. For example, at zero frequency, the characteristic impedance of the cable its direct current resistance; and in the case of an actual cable between New York and the Azores, this resistance is about 4600 ohms. The principal diliiculty in cor recting the distortion of this cable for sig naling speeds above 30 cycles per second, lies in reducing suflicientiy the relatively enor mous amount of gnaling components of the lower frequencies which are transmitted over the cable. This requires the utilization to the fullest extent of shaping at both the transn'iitting; and receiving terminals of the cable. The shunt resistance 21 aids materially in accomplishing this result and is a novel and efficient shaping element.

The immediate purpose of the shunt resistance 21 is to prevent the variable cable impedance from having any appreciable effeet on the circuit consisting of the sending; battery 17, battery resistance 18, shunted condenser 19, and cable and shunt resistamxe 21. In practice, it is found that this purpose is sutliciently well accomplished if resistance 21 has a value of from 50 to 200 ohms. ihe effect of resistance 21 is to cause the application to the cable of the voltage wave form produced by charging the condenser 19 through a practically constant resistance. When, as previously was the practice, the resistance 21 is omitted, the voltage applied to the cable is modified by the changing impedance of the latter in a direction to react unfavorably against the the effect of the series condenser. This may be made more plain if we compute the voltages applied to the cable by various co1nponent frequencies of the signal. In these computations the shunt 20 on the condenser 19 has been neglected as it is not necessary to an understanding of the effectof the cable shunt The measured impedance of the actual loaded cable hereinbefore mentioner. at various frequencies is given in the fol lowing table, where in F is the frequency, R the resistance component of the impedance, X the reactive component of the impedance, and Z the absolute value of the impedance in ohms.

involved in signalin cases, one in which. the resistance shunt 21. was not used, and the other in which the shunt 21 had a resistance of ohms. The

results of this computation are shown graphically in 5 where curve C represents the oltage frequency characteristic of the cable without shunt 21 and curve I), when shunt 521 is used.

The efliciency of the sending condenser may be judged by the effect it has in lower-- ing' the applied voltages at the lower frequencies. For ellicient operation, it is in tial that the voltage of the lower frequency components be reduced in amplitude to a greater extent than the higher frequency components. It is apparent from curve C that without the shunt 21, the sending condenser is practically without effect at frequencies above 20 cycles and may be said to have negligible efliciency over this range, "while with the resistance 21 in circuit, the relation between the voltage applied to the cable and the frequency of the applied volta e, practically a straight line up to cy es per second. The elliciency of the two shaping circuits may be roughly expressed as the relation in each case between the voltage impressed on the cable for the maximum frequency signal component and some other lower frequency which it necessary to suppress. In the case of the ordinary condenser circuit, the voltage at 80 cycles is two and one-half times that at 5 cycles; while in the case where the shunted condenser is used, the voltage at 80 cycles is eleven times that. at 5 cycles. It is thus seen that the sending circuit employing the shunt re sistance 21 is much superior to that of previously known arrangements.

This method of transmitting end shaping is particularly valuable, since it does not cause oscillation of the transmitted voltage, such as would be the case if an attempt were made to produce the same sort of an ellect by means of an inductive shunt.

A similar transmitting equipn'ient (not shown) is provided at the distant end of the cable for transmitting to the receiving; apparatus R, and need not be further described.

The twin core section 6 is connected to the receiving equipment through a novel network which is illustrated by the portion of Fig. 1 between lines X--X and Y-Y. This termination consists of a shielded transformer 25, the secondary winding 26 of which is connected to the input circuit of the amplifier of Fig. 2. The primary wind- 27 is connected to coupling resistance 28 by means an anto-transformer 80. Re sistance 28 is variable up to a maximum of 10,000 ohms. Resistance 29 is variable up to 100,000 ohms. Connected in series with the core 7 is a variable condenser 31 of 0.1 to 10 microfa-rads shunted by a variable recore of grade A iron dust rings.

sistallce .of 10,000 to2,00.0,000 ohms forming net work N1. This network is used to control the amplitude and phase of the lower frequency components of the signaling current. An anti-resonant network N consisting of a variable condenser 33 of 0.1 to 5 microfarads, inductance 34; of 50 to 150 henrys, and a shunt resistance 35 of 1000 to 20,000 ohms, is also connected in series with the core 7 and network N This network N is tuned to a frequency below the signal ing frequency for which the rest of the system is adjusted and is used to reduce the amplitude of this and adjacent components of the signaling current and at thesan'ie time maintain a high impedance termination for the cable at these frequencies. The

adjustment of. the resistance is customarily low enough to insure thatthis network is highly damped,-. and does not superpose anoscillation on the signal. Resistance is also useful in adjusting the very low frequency components of the signal that is those below the range in which condenser 33 and the inductance of coil 34 are effective.

Another network N consisting of a con denser 36 ,of 0.1 to 4: microfarads and inductance. of 1 to 10 henrys, is also connected in series with the conductor 7 and the .two networks N and N?. This network is sharply tuned and is used to eliminate a single interfering frequency outside the range of frequencies essential to signaling. This network is only used when such interfering frequency is present, and

can be removed from the circuit by closing switch 88. Such interfering frequency may come from a number of sources, such as, for example, an electric railroad located in the neighborhood of the terminal stat-ion.

Auto-transformer 30i s yariabI-y connected to the input winding 27 of transformer 25 by way of conductor 40. The point ll of the primary winding is connected to the junction point of resistances 28 and 29. The secondary winding 26 of transformer 25 is surrounded by shield 42 which is connected to the locally grounded terminal of vv ind ing 26. k v i v The auto-transformer 30 may be a coil of about 50 henrys inductance wound on a p 7 These rings have a permeability of approximately 55 are described in an article by Messrs. Speed and Elmen, entitled Lagnetic properties of compressed powderediron, published in the Journal of the American Institute of Electrical Engineers, Vol. 10, July, 1921, cage 59.6. Resistance 29 is preferably of a high .value so that its effect on the circuit .is small; but at adjustments which allow the received signal to produce troublesome oscillations, this resistance may be used to increase the damping of the circuit and so reduce its tendency tooscillate. It should teena e.

be noted that the purpose of this auto-transformer to increase the definition of the signal by -partially suppressing a certain band of frequencies somewhat lower than the signaling frequency which, without this suppression, would cause the received wave to overshoot and distort signals beyond legibility. This is also the purpose of the series anti-resonant circuit N but while the latter is adjusted to be effective at approximately one-third of the signaling frequency, the auto-transformer is usually adjusted to be effective at about two-thirds of the signal frequency. This is accomplished by the proper adjustment of the resistance 28 with relation to the primary inductance and primary to secondary turns ratio of auto-transformer 80. 'lransformcr 30 is connected so that the induced second-- ary voltage opposes the voltage drop across resistance 28, but the adjustment is such that this opposing voltage is negligible except for the band of frequencies which it is desired to suppress.

As an. illustration of the effect of these i'ieiiworks on the arrival curve produced by applying a steady voltage to the tran mitting terminal of the cable, reference is made to the curves of Fig. (5 where curve 10 shows the shape of the received volt-1g at the secondary terminals of transformer 25 when network N and resistance 28 alone are used. Curve F shows the effect on the received voltage of adding network N, while curve shows the effect of adding the autotransformer 30. These curves would normally be superposed, if plotted to the same scale of ordinates; but for the sake of clearness they are plotted separately. Since it is necessary that the arrival curve approximate a square-topped .wave in order that an: distorted signals may be received, it is evident that the speed ,of transmission possible with the circuit employed for obtaining curve G, is much greater than the speed ohtainable with either of the other arrange ments.

A suitable design. for transformer 25 is descrilied in applicants Patent 1,580,972.

supra. The core is of the shell tansformer type and is made up of strips of nickel-iron alloy. The winding is arranged to have very small distributed capacityf Both the primary and secondary windi are made up of pancake sections. liy its]: the larger part of the winding space is occupied by the primary coil, sufficient space being occupied by the secondary coil to give a reasonable primary to secondary turns 'atio when the smallest wire available is used for the scrondary winding. The use of a high resistance secondary coil is permissible on account of the fact that the secondary coil works into practically an infinite impedance. Measurements on an actual transformer at a value of lull current of the order of that encountered in submarine signaling show that its primary inductance is 6300 henrys and its direct cur rent resistance is about 0.28 ohm per henry. ll ith the primary cloL-ed on its normal impedance, the leakage inductance measureifl from the secondary terminals is ot the order of henrys. The ratio of primary reactance to primary resistance is notless than a0 from four to twenty cycles per second. The capacity between the primary sections a jacent to the secondary shield and the i iccondary shield i s of the order of 500 micro u'iicrofarads.

The amplifier of Fig. 2 comprises four stages of electron discharge amplifiers with suitable coupling circuits and signal shaping networks. The first stage annplitied A is provided with a negative grid battery 50 ct three volts. The filament of all the amplifiers are grounded and heated by current from a six-volt battery under the control of rl'ieostats, as shown in Fig. 2.

The output circuit of amplifier 11 coupled to the shaping network o1 by means of resistance 52 which is adjustable in four steps up to a maximum of 102,000 ohms and condenser 53 of 50 mierofarads capacity. ln series with resistance is space current supply battery 13 of 250 volts. The shaping network consists of a primary variable condenser 5% of 0.01 to 0.20 microfarads capacity, secondary variable condenser of 1000 micro-microfarans maximum capacity adjustable resistance 50 of a maximum value oi 300,000 ohms and inductance coil 57 of 10,000 henrys maximum inductance, and a c., oper resistance of about 45,000 ohms.

i1 type of coil which is suitable for autotransformer 57 has a core consisting of permalloy trips built up in the nanm of shell type transformer core in which a small air-gap is included in the magnetic circuit at one end of the central l The winding const ts of seven pancake Motions.

each 0.35 inch thick, and containing 8300 single silk covered copper wire having a reel ance of about 0500 ohms The total copper resnitance is.

re. about $5,000 ohms, while the it CLHDCQ is amaroxnnatcly 10,000 hen embed in applimate it coil of this type is: d

:ants copending application Serial No. 000.109, supra.

The upper terminal of coil is conu ted to the id of amplifier A. The grid of amplifier A is maintained negative with r spect to the filament by means of battery 58 of tnree volts.

The shaping network 51 is not IHlBHLldI a esonant network but comprises an auto- "r'ormer with an abnormally high primary 1ft 'stance. .This resistance is so high in relation to the primary reactance at all of the higher frequency components of the signal that the current in the primary circuit is practically in phase with. the voltage across it. However, the turns ratio of the transformer is so large that the secondary induced voltage for the higher frequency components of the signal adds considerably to the voltage transmitted conduetively to the secondary terminals by the drop in potential across. the primary re sistance. The resulting characteristic of this network 51 is that the lower frequencies are transmitted to the secondary terminals unchanged, while the higher frequencies have their voltage increased substantially. The phase components of the signal are shifted approximately proportionately to their frequency. Under these circumstances, the phase shifts do not change the shape of the signal, but merely retard it bodily in time; but as the amplification is greater for the higher frequencies than for the lower, the attenuation of the cable is partly compensated for. The primary condenser and the secondary condenser are used with caution principally for the purpose of reducing the effect of interference higher in frequency than any of the essential components of the signal.

The amplifier A is coupled to shaping network 59 by means of resistance (50 which is adjustable in four steps up to a maximum of 192,000 ohms and condenser 61 of 10 microfarads capacity. In series with resistance is space current battery B of 250 volts. Shaping network 59 consists of inductance coil 62 shunted by resistance 66 connected in series with condenser 63. The input circuit of amplifier A is connected across the variable portion of potentiometer 6d, the fixed portion of which in series with grid polarizing battery is connected in shuntt-o condenser 63. Inductance coil 02 has a maximum inductance of 100 henrys. Resistance 00 variable up to a maxinu .n of 200,000 ohms. Condenser 63 has a cap-ac ity of 0.01 to 0.2 microfarads. Negative polarizing-g; battery is of 1.5 volts. The potentiometer (i-1 has a maximum resistance of 2 megoms.

Amplifier A is coupled to network (57 by means of resistance 68 which is also variable in four steps up to a maximum of 102', 000 ohms and condenser 69 of 10 micro farads. In series with resistance 0 is space current battery 13 of 250 volts. The

Resistance 72 has a value of mego'lniis. The "negative grid polarizing battery 73 has a potential of 40 volts.

Space current for ampliflier A is supplied by battery B of 250 volts. Amplifier A consists preferably of two vacuun'r tubes connected in parallel; For sin'iplicity one only is shown. The output circuit of amplifier A including battery B extends through a receiving device which may be a siphon recorder as indicated. In the arrangement shown, the indic'ziting device '75 is located a considerable distance from the amplifier and is connected thereto by means or ii cable 76. A second indicating device 77 \Vl'rlt3l1 may also be a. siphon recorder, as shown, is connected in series to the output circuit of the amplifier for moiiitoring purposes.

Networks 59 and 67 may be adjusted so as to consist of a resistance and capacity in series or inductance and capacity iii series or a shunted inductance in series with a capacity, the voltage which is impressed upon the input circuit of the succeeding amplifier being that across the condenser in all cases; Each of the adjustments discriminates against interfering components having frequencies higher than those essential to signaling. In addition, the first adjustment produces a relative advance in phase of the higher frequency components of the signal with respect to the lower, that is, a shift in the samed-irectionas that produced by the cable. The second adjustment may be such as to relatively retard the phases of the components up to a certai frequency and advance them beyond that frequency. The third adjustment may be such as to act in either manner depending upon the relative magnitudes of the threecircuit elements. used for the purpose or increasing the flexibility of the adjustments of the amplifier of: Fig. 2', and in this way pern'iitti-ng the amplifier to operate satisfactorily over a large range of signaling speeds.

In the signaling arrangements known prior to the present invention, it was possible to satisfactorily shape code signals up to a signaling speed of 30 cycles per second, as hereinbetore mentioned. In order to determine the effect of the system upon the differentfrequency components of the signaling curreiit, aterniinating network,

such as that sliown'in Fig. 7, was used in the system oi Figs. 1 and 2 betweenthe lines X-X and 1 -1 According to that arrangement, networks N and N and autotransformer 30 of 1 were omitted and no shaping was employed the amplifier of Fig; 2. The network N of Fig. 7 is identical with the corresponding network of Fig. '1 and consists of condenser 31 and variable resistance 32. The cable is coupled to the primary winding 27 oi: transformer The potentiometer (34 is 25 by means of variable coupling resistance 80. In place of the transmitter 17 at the sending end, various sine wave currents ol different frequencies were impressed upon the cable through condenser 19 shunted by resistance 20. The circuit elements were adjusted to have the following values: Sending resistance 18, 17 ohms; sending condenser 19, 60 microi arads; shunt resistance 20, 5000 ohms; receiving condenser 31 of Fig. 7, 2 microiarads; shunt resistance oi Fig. 7, 400,000 ohms; coupling resistance or Fig. 7, 1,500 ohms; voltage of sine wave source (R. M. 8.), 10 volts.

.lvith the circuit adjustments just given, the curve A of Fig. a]; was obtained, showing that current of approximately 15 cycles was much less attenuated than either the lower or the higher frequencies. This marked diftlierence in the amount of attenuation of the Various frequency components accounted for the distortion of the signals which prevented code reception at signaling speeds above 30 cycles.

In order to equalize the attenuation of the various frequency components, the arrangement of Fig. 8 was substituted for that of Fig. 7 between the lines XX and YY in Fig. 1. A series resonant network N consisting of condenser 81, inductance 82, and resistance 83 was connected between conductors 7 and 9 of the twin core section 0. Resistance Set was connected in shunt to inductance 82. This network was tuned to offer low impedance to current having a frequency of approximately 15 cycles. The circuit elements were adjusted to the following values: Sending resistance 18. 17 ohms; sending condenser 19, (30 microtarads; shunt resistance 20, 5000 ohms; receiving condenser 31, 1. 1 microtarads; receiving resistance 32, 800,000 ohms; resist.- ance 80, 1500 ohms; condenser 81, 11 micro farads; inductance 82, (3.5 henrys; resistance of inductance 82, ohms; resistance 823. 300 ohms; resistance 84, 800 ohms.

ith this arrangement, curve B oi Fig. t was obtained which shows that the alienuation of the diilerent frequency components is more nearly equalized by the arrangement of Fig. 8 than by that of Fig. '7.

The use of the series resonant shunt network N of Fig. 8 while effective in equalizing the attenuation of the various frequency components of the signaling current reduces the terminal impedance of the cable at the frequency to which the series resonant circuit is tuned and correspondingly lessens the impedance to adjacent frequencies. To overcome this difliculty, the arrangement of Fig. 9 was employed. In other words. the shunt series network of Fig. 8 is replaced by the series anti-resonate network N consisting of inductance 34, condenser 33 and resistance \Vith the arrangement of Fig.

IOU

l lfi S) substituted for that portion of Fig. 1 between the lines XX and Y Y, an increase in signaling speed up to about cycles per second was obtained.

With. this arrangement, as the signaling speed was increased above 50 cycles per sec end, there was a tendency for the compo nents of the signaling current which were slightly lower than the reversal frequency, to become excessive and so distort the shape of the receiving signals. In order to overcome this ditiiculty, the auto-transformer 30 was inserted, as shown in Fig. 1. lVith this arrangement, code messages have been receivml over the New Y0i'lAZOres loaded cable at signaling speeds up to cycles per cond. The indications are that higher speeds could be attained providing the interference due to extraneous sources, such as power and lighting circuits, and natural electr :al disturbances could be eliminated or reduced. 1

One or more additional shaping networks, similar to networl-r N but differently adjusted, could be used if the service conditions warranted. Such networks might replace auto-transf0rmer 30. Each would be effective to suppress certain of the lower frequency components of the signal and each would be most effective at a particular frequency orrange of frequencies.

The signaling speed of 60 cycles per second was obtained with an adjustment of the circuit elements of Figs. 1 and 2 as follows: Sending resistance 18, 17 ohms; sending condenser 19, 10 microfarads; sending shunt resistance 20, 10,000 ohms; sending shunt resistance 21, ohms; battery voltage, 60 volts; signaling speed, 10% marking, 60 cycles per second.

Network NInductance 37, condenser 30, 0.17 microfarads.

Wetwork N lnductance Set, 150 henrys; condenser 33, 0.41: mierofarads; resistance 37 7000 ohms.

lletworl: NQondenser 31, (3.8 microfarads; resistance 32, 15,000 ohms; couplf" resistance 28, 1500 ohms; dan'iping ref ance 29, 00,000 ohms; toti-ilnumber of turns in a1ito-transformer 30, 11,000 turns; primary turns of aiito-transformer 2-30, 2000 turns; interstage coupling resistances 60 and 68, each 192,000 ohms.

Network 5l-Primary condenser at, 0.03 microfarads; primary inductance of autotransformer 57, 60 henrys; primary resist-- ance of auto-transformer 57 and resistance 50, 200,000 ohms; total inductance of autotransformer 57, 10,000 henrys; secondary condenser 55, 100 microanicrofarads.

Network 59-Potentiometer 6 1, 2 megohms; inductance 62, open circuited; re sistance 66, 125,000 ohms; condenser 63, 0.01 microfarads.

Network 67Resistance 72 (not adjust- (no henrys and the it'llllfllli'ltll. .i

able), 2 megohms; inductance 70, open circuited; resistance 74-, 125,000 ohms; condenser 71, 0.01 microfarad.

As an alternative to the preferred sending circuit of Fig. 1 that of Fig. 10 may he used. it is similar to the sending arrange ment of Fig. 1 except that the comparatively low resistance 21 of Fig. 1 has con replaced by the series resonant network N consisting of condenser 90, inductance 91, series resistance 92, and shunt resistance 93. The network is adjusted to offer a ion impedance to thefrequcncy components of the signal. which are leastattenuated by the other portions of the cable system. l'l hile th s arrangement shows improvements over systems heretofore known, it is less desirable than the arrangement of Fig. l as it does not give good results due to the fact that it causes partial oscillations to be superposed on the signal and also introduces distortion due to hysteresis in the coil 91.

Still another alternative sending circuit which is preferable to that of Fig. 1 under some operating conditions is shown in Fig. 11. This circuit is identical. with that of l ig. 1 except that very large condenser of several. hundred microfarads is inserted in series with sending shunt resistance 21. This condenser is so large that it has little influence on the action of the shunt resistance at any but the extremely low frequency components of the signal.

As hereinhefore explained the low resistance shunt 21 is important in high speed working, since it greatly increases the effectiveness of the usual sending condenser, but it has the disadvantage of shunting to earth the larger part of the extremely low frequency components of the transmitted signal, thereby requiring that the series condenser at the receiving end of the cable be shunted by a relatively low resistance. Such a low uuce at the receiving terminal objectionable, since it permits a rather strong earth current to flow through the shaping: llttWOllC which is located between the cable he establislrn'zent of this earth currentduring switching from se ding to receiving produces a heavy surge through the amplifier and momentarily displaces the zero of the signal. The insertion of the large condenser 95 materially reduces the strength of earth current and switching surges by permit ing the use of a much higher resistance shunt on the receivin condenser.

in connection with the operation of print ing telegraph equipment over the cable between New York and the Azores, it was found that the use of condenser 95 in series with resistance 21 permitted the value of the resistance shunt 32 on condenser 31 at the receiving station to be increased from 15,000 ohms to 250,000 ohms. The corresponding circuit, a resistance connected in parallel to both said input circuit and auto-transformer, and a. connection from the intermediate terminal of said auto-transformer to said resistance.

13. In a submarine signaling system, a submarine cable, a receiving device having an input circuit ,for r ceiving signaling current, said input circuit being connected between said cable and ground, an auto transformer connected in series with said input circuit, a resistance connected in parallel to both said input circuit and auto-transformer, and a connection from the intermediate terminal of said auto-transformer to an intermediate point of said resistance.

14-. Shaping apparatus for a submarine signaling system, comprising an auto-transformer, a resistance in series with the primary winding of said autdtransformer, a second resistance shunted around said primary winding, signal receiving apparatus connected between said series resistance and the secondary winding of said autotrans former, whereby the voltage induced in the secondary winding may be adjusted to oppose the voltage across said series resistance and the primary winding to any desired extent and for any desired range of frequencies.

15. In a submarine signaling system, a submarine cable, a receiving device comprising an electron discharge amplifier ha 'ing shaping networks for changing the relative amplitudes of the several components of the signaling current, a transformer for impressing signaling current upon said amplifier, and a shaping network connected be tween said cable and the primary winding of said transformer comprising an anti-resonant circuit for reducing interfering current of a frequency above the frequencies essential to signaling, a second anti-resonant circuit for reducing the effect of signaling current of a frequency within the range of essential signaling frequencies, and a shunted condenser for reducing the effect of current of very low frequencies within the range of essential signaling frequencies.

16. A submarine cable loaded with an alloy of nickel and iron having high per meability at low magnetizing forces, signaling apparatus associated therewith. the characteristics of said cable and said apparatus being such that certain frequency components of the signaling current are transmitted thereover with less attenuation than other frequency components, and a network comprising a highly damped antiresonant circuit tuned to said certain frequency components connected in series with said cable at one terminal thereof.

17. A submarine cable loaded with an alloy of nickel and iron having high permeability at low magnetizing forces, sending equipment including a series shunted condenser and receiving equipment also i11- cluding a series shunted condenser so proportioned as to transn'iit with least attenuation components of the signaling current somewhat below a predetermined signaling frequency, and a highly damped anti-resonant circuit connected in series with the signaling current path and tuned to the frequency said least attenuated components.

18. A submarine cable loaded with an alloy of nickel and iron having high permeability at low magnetizing forces, receiving apparatus comprising an electron discharge amplifier, a transformer for impressing signaling current upon the input circuit of said amplifier, a resistance con nected in shunt to the primary winding of said transformer, and a highly damped antiresonant circuit connected in series with the signaling current path between said cable and said resistance and tuned to a frequency lower than the signaling frequency.

19.A submarine cable loaded with an alloy of nickel and iron having high permeability at low magnetizing forces, a re ceiving device having an input circuit for receiving signaling current, said input circuit being connected between said cable and ground, an auto-transformer connected in series with said input circuit, a resistance connected in parallel to both said input circuit and said auto-transformer, and a connection from the intermediate terminal of said auto-transformer to an intermediate point of said resistance.

20. A. submarine cable loaded with an alloy of nickel and iron having high permeability at low magnetizing forces, a receiving device comprising an electron dis charge amplifier having shaping networks for changing the relative amplitudes of the several components of the signaling current, a transformer for impressing signaling current upon said amplifier, and a shaping network connected between said cable and the primary winding of said transformer comprising sharply tuned anti-resonant circuit for reducing an interfering current of a frequency above the frequencies essential to signaling, a highly damped anti-resonant circuit for reducing the effect of signaling cuiu'ents of a band of frequencies within the range of essential signaling frequencies, and a shunted condenser for reducing the effect of current of very low frequency within the range of essential signaling frequencies.

21. In a cable signaling system comprising a cable, an impulse transmitter connected to said cable through a sending condenser, and a path to earth having an impedence low in comparison with the characteristic impedance of the cable connected at a point between said cable and said condenser, said'p'ath comprising a low resistance and a large condenser. y

22. In-a cable signaling system, a submarine cable, transmitting apparatus connected thereto comprising an impulse transmitter and a shunted sending condenser connected in series, and a series circuit connected to sand cable 1n shunt to said transmitting apparatus, said circuit comprising a low resistance and a condenser so large that its effect upon said series circuit except at very low frequencies is negligible.

In Witness whereof, I hereunto subscribe my name this 15th day of September, A. 1)., 1925.

AUSTEN M. CURTIS. 

